ROADM enables the drop, add and direct-through of channel wavelengths locally through software configuration, and enhances the transmission flexibility of optical network services. ROADM systems in the related art have a Colourless Directionless Contentionless (CDC) function. The traditional wavelength division multiplex system employs a fixed grid technology, in which a channel grid generally is fixed to 50 GHz or 100 GHz. The beyond 100 GHz transmission technology generates a flexible grid (or gridless) requirement, that is to say, the width of the channel grid is flexible so as to adapt to wavelength division multiplex transmission requirements of different modulation codes and different ratios. The CDC function of the ROADM evolves to a Colourless Directionless Contentionless Gridless (CDCG) or Colourless Directionless Contentionless Flexible (CDCF) function. The flexible grid technology has been primarily standardized by the International Telecommunication Union-Study Group 15 (ITU-SG15) according to G.694.1 standard in February, 2011, and the internal release of the draft standard document is V1.2. The frequency-slot nominal central frequency is specified to be 193.1+n×0.00625, where n is an integer; the frequency width is specified to be 12.5 GHz×m, where m is a positive integer. For convenient description, generally the ROADM system employing a flexible grid technology is called a Flex ROADM system for short. As shown in FIG. 1, in a fixed-grid network, the spacing between two adjacent channels of a wavelength bearing services of different rates is fixed to 50 GHz or 100 GHz; meanwhile, each wavelength is allocated with a fixed spectrum bandwidth resource of 50 GHz or 100 GHz. At this time, the wavelength bearing services of different rates is expressed by the central frequency of f=193.1+n×C.S defined by ITU-TG.694.1 only (C.S is the abbreviation of Channel Spacing, which indicates the fixed spacing between two adjacent channels; n is an integer; n×C.S represents an offset relative to 193.1 THz). However, in a flexible-grid optical network, high-speed services can be allocated with more spectrum bandwidth resources according to the actual condition, and low-speed services are allocated with fewer but sufficient spectrum resources; in this way, the bandwidth utilization of network is greatly improved. However, in high-speed services, one channel might include one or more subcarriers, which may be allocated on a continuous spectrum or a discontinuous spectrum. As shown in FIG. 1, one spectrum bandwidth is 8×12.5 GHz, including 4 continuous subcarriers, each subcarrier being of 25 GHz spectrum bandwidth. Due to the CDC complexity in the ROADM system, when high-speed service spectrum is transmitted in the Flex ROADM system, problems such as subcarrier loss, subcarrier being allocated to an error path, incomplete filtering or mutual conflict of subcarriers are easy to occur.
Different from the traditional optical network, the beyond 100 GHz optical transport network not only introduces the flexible grid technology, but also possesses a multi-carrier optical transmission technology and a higher Digital Signal Processor (DSP) processing capability, and thus has a configurable/programmable feature. The programmable feature means changes can be made according to requirements, for example, different spectrum efficiencies and compensation algorithms can be selected according to different link states at the line side of the system, a wavelength selection component in the ROADM node of the system selects different grid widths and filtering shapes according to different signal spectrum widths and concatenation levels. The receiving end in the system selects a corresponding DSP algorithm according to different Baud rates and modulation formats. The above-mentioned configuration information is transmitted to each node of the system by a network management system. When the sending side configuration (such as modulation format and subcarrier multiplexing mode) of the sending end of the line side of the system is changed by the network management system according to the link state, correspondingly, the network management system also needs to change the configuration of each ROADM node and the receiving end in the link. The ROADM optical network uses the network management system to configure all nodes in the optical network. These configurations are programmable and can be changed multiple times as needed, especially in the beyond 100 GHz applications. The increase in configuration work load leads to a big error probability of configuration; however, in existing networks, there is no effective method to judge or monitor whether the configuration information is erroneous or whether an error occurs during the transmission or transfer process and the location of the error.
Meanwhile, in the wavelength division multiplex system, each optical channel or optical wavelength is loaded with a pilot tone signal, which can be used for realizing multiple special applications. Certain study has been made for the application of the pilot tone signal in the industry. The pilot tone signal sometimes is also called a low-frequency dither signal, and the impact of the pilot tone single loaded in the wavelength signal on the transmission performance of the channel almost can be neglected. In related art, the study made on the pilot tone signal mainly includes: 1) in an optical network element based transport network layer, the pilot tone signal is used to realize the confirmation and power management of a wavelength channel required by fault management in the wavelength division multiplex system; 2) for example, a method for monitoring the performance of an optical amplifier is provided in the method and device for monitoring the performance of an optical transmission system, that is, a pilot tone signal with a known modulation depth is monitored to realize the pre-estimation of signal and noise component of the optical amplifier; 3) in the signal tracking and performance monitoring of a multi-wavelength optical network, a scheme of realizing an on-line wavelength route tracking in a wavelength division multiplex network is proposed, that is to say, each wavelength is modulated by one unique pilot tone signal and digital information is encoded by frequency-shift keying; the pilot tone signal can be monitored at any site in the optical network and thus the wavelength route information of the entire network can be acquired. However, the above applications generally are designed for the fixed-grid ROADM system and are not applicable to the monitoring of flexible-grid and subcarrier. In view of the above problems, no solution has been put forward so far.